Webb Science Simulations: Planetary Systems and Origins of Life

on October 28, 2010

Supercomputer simulations of planeratry evolution.

Part 1: Turbulent Molecular Cloud Nebula with Protostellar Objects

The Advanced Visualization Laboratory (AVL) at the National Center for Supercomputing Applications (NCSA) collaborated with NASA and Drs. Alexei Kritsuk and Michael Norman to visualize a computational data set of a turbulent molecular cloud nebula forming protostellar objects and accretion disks approximately 100 AU in diameter, on the order of the size of our solar system. AVL used its Amore software to interpolate and render the Adaptive Mesh Refinement (AMR) simulation generated from ENZO code for cosmology and astrophysics. The AMR simulation was developed by Drs. Kritsuk and Norman at the Laboratory for Computational Astrophysics.

The AMR simulation generated more than 2 terabytes of data and follows star formation processes in a self-gravitating turbulent molecular cloud with a dynamic range of half-a-million in linear scale, resolving both the large-scale filamentary structure of the molecular cloud (~5 parsec) and accretion disks around emerging young protostellar objects (down to 2 AU).

Part 2: Protoplanetary Disk and Planet Formation

The Advanced Visualization Laboratory (AVL) at the National Center for Supercomputing Applications (NCSA) collaborated with NASA and Dr. Aaron Boley to visualize the 16,000 year evolution of a young, isolated protoplanetary disk which surrounds a newly-formed protostar. The disk forms spiral arms and a dense clump as a result of gravitational collapse. Dr. Aaron Boley developed this computational model to investigate the response of young disks to mass accretion from their surrounding envelopes, including the direct formation of planets and brown dwarfs through gravitational instability.

The main formation mechanism for gas giant planets has been debated within the scientific community for over a decade. One of these theories is 'direct formation through gravitational instability.' If the self-gravity of the gas overwhelms the disk's thermal pressure and the stabilizing effect of differential rotation, the gas closest to the protostar rotates faster than gas farther away. In this scenario, regions of the gaseous disk collapse and form a planet directly. The study, presented in Boley (2009), explores whether mass accretion in the outer regions of disks can lead to such disk fragmentation. The simulations show that clumps can form in situ at large disk radii. If the clumps survive, they can become gas giants on wide orbits, e.g., Fomalhaut b, or even more massive objects called brown dwarfs. Whether a disk forms planets at large radii and, if so, the number of planets that form, depend on how much of the envelope mass is distributed at large distances from the protostar.

The results of the simulations suggest that there are two modes of gas giant planet formation. The first mode occurs early in the disk's lifetime, at large radii, and through the disk instability mechanism. After the main accretion phase is over, gas giants can form in the inner disk, over a period of a million years, through the core accretion mechanism, which researchers are addressing in other studies.

Thanks to R. H. Durisen, L. Mayer, and G. Lake for comments and discussions relating to this research. This study was supported in part by the University of Zurich, Institute for Theoretical Physics, and by a Swiss Federal Grant. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center.

This visualization shows a visual tour of a nebula, a turbulent molecular cloud with multiple protostellar objects, to a close-up view of a single protoplanetary disk entering a phase of violent instability, which forms clumps that may become planets or brown dwarfs. Drs. Alexei Kritsuk and Michael Norman provided the computational data of the turbulent molecular cloud. Dr. Aaron Boley provided the computational data for the isolated protoplanetary disk.